1. Field of the Invention
This invention relates to a method and apparatus for monitoring and controlling a chemical process for manufacturing semiconductor devices and more particularly to detection of the condition of a chemical substance employed in such a chemical process.
2. Description of Related Art
In-line real-time testing of chemicals using density, color, spectroscopy, pH, etc. is generally known and used in many industries, including the chemical and semiconductor industries.
U.S. Pat. No. 5,262,961 of Farone for "Method for Monitoring and Controlling a Chemical Process" shows a method of monitoring and controlling a chemical process by measuring the concentration of the process reactants and products using spectrometric technology, but not in a semiconductor manufacturing process.
U.S. Pat. No. 5,401,664 of Larson et al "Analytical Method for Determining Concentration of Decomposition Products in Solvent Used for Solvent Extraction" describes an analytical method for determining the concentration of extraction. However, this invention does not appear to be a real time measurement.
Current methods of detecting the life-time of reacting chemicals are as follows:
1. Chemical analysis of contaminated elements added in the chemical, which is really time-consuming way, and is not applicable to sudden chemical variation. PA1 2. Unscientific life-time estimate with respect to numbers of runs or lots passed through the chemical, which must be not a cost effective method.